The correct answer is B) Bulb and dovetail. This is the correct answer because bulb and dovetail is a common method of power turbine blade retention used in the marine and aviation industries. The bulb and dovetail design securely locks the turbine blades into the rotor disc, providing a strong and reliable connection. The other answer choices are not correct. Riveting and fir-tree are not common methods of turbine blade retention. Fir-tree and bolting, while used in some applications, is less common than the bulb and dovetail design. Bulb and bolting is also a valid method, but it is not as widely used as the bulb and dovetail approach.